Flow error weirdness

[hobofett25]

Hopefully someone here can help me. I've got a 2006 Morgan tub. I can get the exact model number if you need it. 

Here's the issue I am having. When the tub is warming up, everything runs fine, low power/circulation mode, high power... everything. Tub heats up fine. 

However, once the tub gets up to temp and goes into low flow mode, it shuts down completely. Then when the temp drops below what it is set for I can hear the pump hum, but I get zero flow. After a few seconds the tub shuts itself down and I get the three flashing dots on the display. 

I've checked for air lock and replaced the filter, so those aren't the problem. 

For example: If the water temp reads 95 and I set the temp for 101, everything works fine. I can press the pump button to cycle between high and low flow. If I put it in low flow, it heats up, reaches the set temp and shuts down. When the temp drops below 101 I hear the motor hum, but it isn't turning and there is zero flow, till it shuts down and throws an error code. 

I thought maybe the capacitor, but low and high work fine when it is trying to reach temperature. I hope that makes sense. Any ideas would be very much appreciated